Noble metal alloy adapted to receive porcelain cladding, artificial dental constructions and method of preparing the same



Dec. 3, 1968 E. WAGNER ETAL 3,413,723

NOBLE METAL ALLOY ADAPTED TO RECEIVE PORCELAIN (IL-ADDING. ARTIFICIALDENTAL CONSTRUCTIONS AND METHOD OF PREPARING THE SAME Filed Jan. 30,1963 514 440 Was/V5115 INVENTQRS 14444725? 'rQKST 4001406 P/FWLOMATTORNEYS The present invention relates to novel noble metal alloyswhich are especially adapted to have porcelain fired on the surfacesthereof for dental purposes and to artificial ceramic dentalconstructions of a novel composition especially of the ceramic layer andadaption of this ceramic layer to the metal substrate. Further theinvention relates to a ceramic covering directly fired on a metal alloysubstrate.

Attempts have been made for some time to combine noble metal alloys withdental ceramic masses in the production of crowns and bridges for use inthe front tooth region by firing dental ceramic masses on caps orstructures of platinum iridium alloys which were either cast or solderedtogether from Wires or strips. Although the dental work thus clad on thenormally visible surfaces thereof were entirely satisfactory from anesthetic as well 30 as a functional viewpoint, they did not meet withcommercial success as the processing techniques were very difficult andas, in view of the differences in the mechanical and physical propertiesof the ceramic masses and the 9 alloys, failures often occurred.

Most recently, attempts have been made to camouflage single crowns byfiring ceramic masses onto the visible labial side thereof or by castingnoble metal alloy structures on previously produced porcelain facets.The porcelain masses, however, were not satisfactory from 21 cosmeticviewpoint and the alloys which are known therefore either are of too lowstrength or were difficult to cast in view of their very high meltingpoint range.

The usual noble metal dental alloys, which are based on gold, silver andcopper or palladium, silver and copper and often also contain additionsof platinum metals, do not meet the requirements which must be met by analloy upon which ceramic masses are to be fired, namely, that thesolidus point of such alloys must be over the temperature required forfiring the ceramic masses thereon and furthermore no oxides can beformed, while the ceramic masses are fired thereon, which react with theceramic masses and discolor them. On the other hand, the formation ofbonding oxides to a moderate degree is desired for effecting a bondbetween the ceramic masses and the alloy. The alloy furthermore mustpossess a sufficiently high strength as even very slight elastic orplastic changes in shape can lead to spalling off of the ceramic massesbecause of the differences in the mechanical and physical properties ofthe alloys and the ceramics.

Finally, it is also desirable that the alloys have as yellow a colortone as possible so that they do not contrast too greatly with thedental work in the less visible portions of the month which is in itsentirety produced from gold alloys.

In the last few years special alloys adapted to have dental ceramicmasses fired thereon have become known, but they met the requirements toonly a limited extent. Alloys which can consist of platinum metals havea very high melting range and as a consequence can only be nited StatesPatent 0 Patented Dec. 3, 1968 melted and cast with difficulty, if atall, with the usual equipment of a dental technical laboratory. Also,their color is not very pleasing. Also, at times, the content of basemetals in such alloys is so high that discolorations occur when theceramic masses are fired on.

Alloys composed of about 85% gold, 05% of palladium and up to 15% ofplatinum adapted to have ceramic masses fired thereon, it is true, areeasy to melt and their color tone meets the requirements. However, theyare relatively soft and as a consequence are not suited for bridges.

Alloys have also become known which in addition to the constituentsindicated above also contain up to 5% of silver and small quantities ofup to about 1% of indium and/or tin. These alloys despite some favorableproperties still possess appreciable disadvantages. The coarse graineddental castings during firing on of the ceramic masses usually tend to afurther coarsening of grain structure by recrystallization. As aconsequence, the strength thereof is reduced and the inhomogeneity ofthe individual crystals usually linked with the coarse grained structurecan lead to discolorations in the mouth.

It is known that the grain structure of gold alloys even thosecontaining palladium and platinum both in as cast and in recrystallizedstate can be refined by the addition of small quantities of metals suchas iridium, rhodium and ruthenium. The grain refining effect decreasessharply with increasing melting or casting temperature so that theeffectiveness with alloys of the above composition remains doubtful.

According to the invention it was unexpectedly found that a smalladdition of rhenium to alloys essentially consisting of gold, platinum,indium and tin and, if desired, can also contain small quantities ofpalladium, silver, iridium, copper and/or zinc will cause a considerableimprovement in the properties of such alloys which evidently essentiallydepends upon a very thorough grain refinement. It was also found thatthe bond of ceramic masses to such alloys is noticeably improved by theaddition of the rhenium. The alloys concerned essentially consist of80-90%0f gold, 515% of platinum, 0.1-2% of indium, 0.1-2% of tin andODS-1% of rhenium. Rheniurn contents of 0.1 to 0.5% are especiallyadvantageous. The alloys can also contain up to 5% of palladium, up to5% of silver, up to 1% of copper, up to 0.5% of zinc and/or 0.05 to .5%of iridium. Especially good results are obtained with alloys containing0.5 to 5% of palladium.

In order to show the influence of the addition of rhenium according tothe invention, the following Table 1 gives the grain fineness measuredin grain count per mm. and Vickers hardness values are given for alloysA and B of the following composition:

1 15 minutes 800 C. 15 minutes 800 C.+15 minutes 500 C. 3 15 minutes 950C. 4 15 minutes 950 C.+15 minutes 500 C.

As can be seen from such table that a notable grain refinement whichconsiderably improved the strength and homogeneity of the alloy wasachieved practically without causing any change in the hardness values.

A further considerable advantage of the alloys according to theinvention as already indicated above resides in the better bondsobtained to porcelain masses fired thereon. In order to determine thebond, platelets of the various alloys measuring about 10 x 6 x 4 mm.were provided on one side with a porcelain coating fused on at 950-1000C. The samples were then embedded in a synthetic resin so that theporcelain clad side was directed upwardly and such porcelain clad sidethen subjected to the action of a 50 g. falling hammer which was allowedto drop upon the porcelain surface from varying heights. At first theheight from which the falling hammer was dropped was increased by 10 cm.measurements until a height of 60 cm. was reached and then the hammerwas repeatedly dropped from such height until the porcelain coatingsplintered off.

In these tests, alloys of compositions A and B concerned in Table l wereagain employed as Well as a further pair of alloys C and D of thefollowing compositions were employed:

Au Pt Pd Ag In Sn I1 Re The porcelain coatings on the test pieces in oneseries were fired thereon under normal atmosphere (series a) and in theother series they were fired thereon under vacuum (series b).

The results obtained are given in the following table:

The increased resistance of the porcelain coated rhenium containingalloys according to the invention against the splintering off of theporcelain when subjected to impact clearly indicates the specialsuitability of the alloys to receive fired on porcelain coverings inview of the improved bond to the porcelain obtained.

The porcelain coverings which can be fused on the alloys according tothe invention are of compositions usually employed for these purposes.

Preferred porcelain coverings fused on alloys result in artificialceramic dental constructions, as specified hereunder. Theseconstructions are particularly suited for the replacement of missingteeth or for capping existing teeth which may be damaged. The noveltooth structures are distinguished by the fact that, on the one hand,they can be prepared by novel working methods in a facilitated mannerand are especially adapted for individual preparation by the dentist inthe laboratory and, on the other hand, they exhibit novel and improvedoptical and physical characteristics due to a novel compositionespecially of the ceramic layer and adaptation of this ceramic layer tothe metal substrate.

The requirements of dental poreclains, particularly with respect totheir physical and optical characteristics, are numerous and exacting.Among the factors of importance are, for example, coverage of the colorrange of the natural teeth, suflicient translucency, compatibility withthe tissues, insolubility, mechanical strength, bond strength ofindividual structural parts of the artificial tooth to one another,suitable fusion intervals, satisfactory performance of the porcelain,e.g. with respect to its mineralogical structure and its coeflicient ofexpansion during fusion to the metal, etc.

The difiiculties indicated above only by way of allusion and encounteredin the direct preparation of artificial ceramic teeth by fusingporcelain onto metal substrates had the result that the problem ofpractical preparation of such tooth structures is considered as beingsolved on principle only recently in the art. Up to the present, thedental profession has made shift either with completely metallicauxiliary constructions or with restorations Where a separately formedand fired ceramic covering was bonded to a performed auxiliary metallicpart. The shortcomings of these techniques had the result that recentlyseveral suggestions have been made recommending direct firing of atooth-like enamel onto a metal substrate. Although an improvement wasobtained by this technique. it appeared that the quality of these dentalconstructions had become poorer with respect to the cosmeticestheticeffect. Therefore, attempts have recently been made of improving thisoptical-esthetical effect of artificial teeth of this kind. Theinvention relates to tooth constructions which give particularly goodresults just in this respect.

It is long known that the coefficient of expansion of the dentalcomposition must be adapted to that of the metal. In particular, it isknown that the enamel should have a somewhat lower coeflicient ofexpansion than the metal because the resistance to pressure of allsilicates, as is known, must be substantially higher than the tensilestrength and, therefore, the outer ceramic layer of the artificial toothmust always be under compressive stress.

However, the artificial tooth structures known up to the present andprepared by the techniques described above invariably exhibitunsatisfactory optical-cosmetic characteristics. The art was notsuccessful so far in imitating the esthetic effect of the natural toothin the tooth structures of the type described in a manner such that anactually unobstrusive use of these artificial tooth structures,particularly in the visible part of the set of teeth would have beenpossible. A substantial reason for this resides in the following fact:When using a metal substrate in the artificial tooth, it is necessary toremove the optical effect of this metal which shows through with agray-golden shade by means of an inner opaque covering layer. Inpractice, it has been necessary up to the present although the contraryis claimed in literature, to apply opaque enamel layers of relativelygreat thickness as a first covering to the metal core in order toprevent the metal effectively from showing through. This resulted in arelative restriction of the naturally available space for thetranslucent ceramic dental composition which imitates the tooth core andthe tooth enamel so that the natural esthetic and optical effect couldnot be attained with such remaining space.

It is an object of the present invention to provide novel artificialtooth structures where a ceramic covering is directly fired onto asubstructure of metal alloys, the tooth structures of the inventionbeing distinguished by the fact that they represent products of highcosmetic quality which also satisfy all other requirements of suchceramic masses used for this purpose. In particular, it appeared thatmulti-layer artificial tooth structures can be prepared advantageouslywhen using specific components in the enamel layers forming the coveringof the artificial tooth while observing specific relative proportions byweight of the individual components. More particularly, the inventionrelates to artificial tooth structures which comprise at least twoceramic enamel layers fired onto the metal substrate, viz. an opaqueenamel layer in direct contact with the metal, this layer beingimpermeable to light and, due to its outstanding optical activity, needsbe only very thin, and a superimposed covering layer of a translucentenamel composition which, in a manenr known to persons in the art, maybe colored at least partially with pigments. In this manner, a layerrepresenting the tooth core and a clear enamel layer especially arrangedin the cutting edges of the teeth are obtained.

The accompanying drawing shows a cross-section of a dental crownembodying the subject matter of the present invention.

In such drawing the dental alloy substrate 1 supports the opaque andtranslucent porcelain enamel coatings 2 and 3 which have been firedthereon.

Accordingly, one embodiment of the invention relates to multi-layerartificial tooth structures of any kind as replacement of missing teethor for capping existing teeth, said structures comprising a metalsubstrate onto which at least two enamel layers are fired andcharacterized in that the metal substrate is coated with an opaqueenamel base layer which is preferably thin and has a composition withinthe following ranges (based on the weight of the opaque base layer):

Percent S 48 to 59 A1203 t0 F6203 t0 TiO 2.70 to 3.30 CaO 1.20 to 1.45 K0 8.40 to 10.30 Na O 5.70 to 7.00 F 0.00 to 0.50 ZrO 1.20 to 1.50 SnO4.30 to 5.25 B205 to and which is surrounded by a translucent coveringenamel layer having a composition within the following ranges (based onthe weight of the translucent covering enamel):

Percent SiO 54.70 to 67.00 A1203 to K 0 8.70 to 10.60 Na O 6.60 to 8.10CaO 1.70 to 2.10 F 0.00 to 0.50 TiO 0.25 to 0.29 Fe O 0.045 to 0.055

Particularly favorable results in the construction of the novel toothstructures are obtained if the two layers give about the followinganalytical values:

Opaque base enamel Percent SiO 53.64 A1 0 18.18 F6203 TiO 2.18 CaO 1.32K 0 9.35 Na O 6.35 F 0.25 ZrO 1.36 SnO 4.76 B 0 1.34

Translucent covering enamel Percent SiO 60.80 A1 0 19.36 K 0 9.66 N320CaO 1.91 F 0.26 TiO 0.26 PC2013 Deviations from these specific valueswithin the ranges given above may be desirable in order to obtain betteradaptation of the physical characteristics of the enamel layers to theparticular metal alloy used, it being especially possible, for example,to influence the coefficient of expansion of the enamel by varying itscomponents in a manner known per se. It is possible in this manner tomask out successfully any suitable metal alloy combination discussedhereafter in greater detail by means of a suitable covering enamel inaccordance with the invention.

Due to the fact that, in accordance with the invention, only extremelythin opaque covering enamel layers are necessary for efficiently maskingout the metallic structure, it is possible to apply the translucentdentine enamel layer which, if desired, may be pigmented in conventionalmanner and also the translucent enamel layer imitating natural toothenamel with a comparatively greater thickness than that of the opaquebase enamel layer. This efficiently aids the improved esthetic-opticaleffect due to the novel and specific enamel compositions.

Alloys which are particularly suitable as substrate for the purposes ofthe invention chiefly include gold, platinum and palladium base alloys.However, base metal alloys known for use in dentistry may also beemployed. All of these alloys are readily available and can be easilyhardened under control. They are free from corrosion phenomena and mildto the tissue of the oral cavity. Their melting points rangesubstantially lower than those of the previously used platinum-iridiumalloys. This results in considerable improvement of the precision of thecasting.

Particularly preferred as metal substrate for the purposes of theinvention are specific alloys containing rhenium as described before.The enamel layers of the invention, particularly the composition,referred to as particularly preferred, of the opaque mass and of theassociated transparent covering mass, have been found to have anoutstanding bond strength to these metal alloys so that artificial toothstructures of excellent resistance to mechanical stress are obtained.

As mentioned above, the specific composition of the enamel masses iscritical for the novel effect in physical and especially also inoptical-esthetic respect. A very essential feature of these masses arethe relative proportions of the alkali metal oxides present. It has beenfound surprisingly that, in contrast to statements in literature dealingwith the prior art, just a relatively high content of sodium is criticalfor the novel elfects described. Accordingly, the enamels of theinvention are characterized by relatively high contents of Na O. As wasfound surprisin-gly, corresponding glasses which contain very much lesssodium and instead much more potassium as compared with sodium do notresult in products having a comparable natural appearance. This factcould not be predicted.

The invention does not only comprise the finished tooth structures butalso the preparation of both the opaque mass and the transparent mass.Improved technical results are in fact not only obtained with thecombination as described above. Advantages are also obtained if, forexample, the opaque mass is used as such in dentistry even if othercombination elements are simultaneously used in preparing artificialtooth structures.

Preparation and processing of the raw enamel masses to the finishedartificial tooth may be effected by techniques conventional in ceramicdentistry. Thus, if desired, conventional opacifiers and coloringpigments known to persons in the art may be added. Processing of thestarting masses, e.g. for quantity preparation of artificial teeth, maybe effected by methods usual in dental industry.

However, the invention also comprises a novel working method which isparticularly suitable for dentists operating on a small scale on anindividual basis. It has been found that it is possible with thecomponents of the invention described above to prepare individuallyshaped dental constructions without the necessity of special technicalequipment. Thus, the enamel can be applied manually to individuallyshaped metal substrates adapted to the requirements and firing onto themetal can be effected with or without the use of reduced pressure. Thispossibility of preparing on a small scale individually shaped ceramicdental constructions which are outstanding in physical and opticalrespect opens a new and important field in dentistry.

What is claimed is:

1. Dental alloy adapted to have porcelain coverings fired thereonconsisting essentially of 80 to 90% of gold, 5 to 15% of platinum, 0.1to 2% of indium, 0.1 to 2% of tin and 0.05 to 1% of rhenium.

2. Dental alloy adapted to have porcelain coverings fired thereonconsisting essentially of 80 to 90% of gold, 5 to 15% of platinum, 0.1to 2% of indium, 0.1 to 2% of tin and 0.1 to 0.5% of rheniurn.

3. Dental alloy adapted to have porcelain coverings fired thereonconsisting essentially of 80 to 90% of gold, 5 to 15% of platinum, 0.1to 2% of indium, 0.1 to 2% of tin, to of palladium, 0 to 5% of silver, 0to 1% of copper, 0 to 0.5% of iridium, 0 to 0.5% of zinc and 0.05 to 1%of rhenium.

4. Dental alloy adapted to have porcelain coverings fired thereonconsisting essentially of 80 to 90% of gold, 5 to of platinum, 0.1 to 2%of indium, 0.1 to 2% of tin, 0.5 to 5% of palladium and 0.05 to 1% ofrhenium.

5. A multi-layer artificial dental construction comprising a metalsubstrate and an enamel facing fired on and directly bonded to saidmetal substrate comprising a first opaque enamel base layer essentiallyconsisting of the following composition:

Percent by weight 6. A multi-layer artificial dental constructionaccording to claim 5 in which said enamel layers consist essentially ofthe following compositions in percent by Weight:

Opaque base enamel Percent SiO 53.64 A1 0 18.18 F6 0 TiO 2.98 CaO 1.32 K0 9.35 W 3'32 2 ZI'OZ S1102 4.76 B 0 1.34

Transparent covering enamel SiO 60.90 A1 0 19.36 K 0 9.66 Nazo CaO 1.91

8 Transparent covering enamel-Continued Percent TiO 0.26 Fe O 0.05

7. Multi-layer artificial dental construction according to claim 5 inwhich said transparent covering enamel layer is subdivided into aconventionally pigmented dentine layer and a non-pigmented enamel layer,said non-pigmented enamel layer being especially present in the cuttingedges of the tooth.

8. Multi-layer artificial dental construction according to claim 5 inwhich said transparent covering enamel layer is applied with acomparatively greater thickness than that of the opaque enamel baselayer, the thickness of said transparent covering enamel layer beingsuch as to obtain improved optical-cosmetic effects in the artificialtooth.

9. Multi-layer artificial dental construction according to claim 5 inwhich said metal substrate is composed of alloys mainly based on gold,platinum and palladium.

10. Multi-layer artificial dental construction according to claim 5 inwhich said metal substrate is an alloy consisting of to of gold, 5 to 15of platinum, 0.1 to 2% of indium, 0.1 to 2% of tin and 0.05 to 1% ofrhenium.

11. An opaque enamel for use in multi-layer artificial dentalconstructions having a metal substrate and an enamel facing fired ontosaid metal substrate consisting essentially of the followingcomposition:

Percent by weight 12. An opaque enamel for use in multi-layer artificialdental constructions having a metal substrate and an enamel facing firedonto said metal substrate consisting essentially of the followingcomposition:

Percent by weight S10 53.64 A1 0 18.18 F203 TiO 2.18 OaO 1.32 K 0 9.35$3.20

2 0. s ZIO 1.36 SnO 4.76 B 0 1.34

13. A transparent enamel for use in multi-layer artificial dentalconstructions having a metal substrate and an enamel facing fired ontosaid metal substrate consisting essentially of the followingcomposition:

Percent by weight SiO 60.80 A1 0 19.36 K 0 9.66 N320 CaO 1.91 F 0.26 TiO0.26 Fe O 0.05

(References on following page) 9 10 References Cited 2,000,285 5/1935Hoffmann 10635 UNITED STATES PATENTS 2,937,099 5/1960 KIltSChfil 106-359/1962 Weinstein et a1. 32-3 FOREIGN PATENTS 5/1922 Fahrenwald 75-465 51,106,966 5/1961 Germany.

12/1942 Leuser 75-165 4/1961 Coleman et aL 32 12 LOUIS G. MANCENE,Przmary Examiner.

9/1962 Weinstein et a1 32-12 CHARLES R. WENTZEL, Assistant Examiner.

1. DENTAL ALLOY ADAPTED TO HAVE PORCELAIN COVERINGS FIRED THEREONCONSISTING ESSENTIALLY OF 80 TO 90% OF GOLD, 5 TO 15% OF PLATINUM, 0.1TO 2% OF INDIUM, 0.1 TO 2% OF TIN AND 0.05 TO 1% OF RHENIUM.